Polymeric water-soluble thickening agents have been extensively used for thickening aqueous based systems containing electrolytes or a dispersed phase including coatings, e.g., latex paints, printing pastes for textiles, bleaching agents, alkaline liquors or paint removers as well as high solids content products like spackle, cements, grout and the like. Further important applications relate to the production of petroleum and ores, as filtration aids or flocculents, and found use in working fluids such as hydraulic fluids and metal working fluids.
In aqueous coating compositions, such as latex paints, it is important to control the rheology to obtain proper flow and leveling with a minimum of dripping and spattering. In other compositions Newtonian flow thickeners are required because of the high shear involved in their use.
Cellulose ethers, alkali soluble latex copolymers, copolymers of acrylic and methacrylic acids and esters which have a portion of the hydrogen ions of the copolymer carboxyl groups replaced with ammonium or alkali metal ions have been used as thickeners as well as other types of polymeric thickeners which contain various carboxylic acid groups which can be solubilized in water by neutralization with a water-soluble base.
A solid styrene-maleic anhydride-vinylbenzyl ether terpolymer soluble at high pH and useful as a thickener for aqueous solutions, in spite of excellent rheology, has had limited use as a paint thickener because of stability problems and cost.
U.S. Pat. No. 4,384,096 discloses a pH responsive thickener comprising an ethylenically unsaturated carboxylic acid, at least one ethylenically unsaturate monomer, and an ethylenically unsaturated surfactant copolymerizable therewith. The surfactant is an alkylphenoxypoly(ethyleneoxy)ethyl acrylate. Similar systems are disclosed in U.S. Pat. Nos. 4,138,381; 4,268,641; 4,668,410; 4,769,167; 5,086,142; and 5,192,592.
It is also known that water soluble polymers of the same type as disclosed in the preceding patents can be used in the formulation of synthetic and semi-synthetic hydraulic fluids to adjust the viscosity to the proper level to achieve technical requirements. See U.S. Pat. Nos. 4,668,410 and 4,769,167.